ch. xxn.] 



ST. CASSIAN BEDS, UPPER TRIASSIC. 



437 



Genera of Fossil Mollusca in the St. Cassian and Hallstadt Beds. 



Common to Older Rocks. Characteristic Triassic Genera. Common to Newer EoefcA 



Cyrtoceras. 



Orthoceras. 



Goniatites. 

 *Loxonema. 

 *Holopella. 



Murchisonia. 



Euomphalus. 



Porcellia. 

 *Megalodon. 



Cyrtia. 



The genera marked by an asterisk are given on the authority of Mr. Suess, the 

 rest on that of Mr. Woodward from fossils of the St. Cassian rocks in the British 

 Museum. 



Ceratites. 



Ammonites. 



Scoliostoma (or 



*Belemnites, 



Cochlearia). 



*Nerin9ea. 



Naticella. 



Opis. 



Platystoma. 



Cardita. 



Isoarca. 



Trigonia. 



Pleurophorus. 



Myoconchus. 



Myophoria. 



Ostrea. 1 sp. 



Monotis. 



Plicatula. 



Koninckia. 



Thecidium, 



The first column marks the last appearance of several genera which 

 are characteristic of Palaeozoic strata. The second shows those genera 

 which are characteristic of the Upper Trias, either as peculiar to it or 

 as reaching their maximum of development at this era. The third 

 column marks the first appearance of genera destined to become more 

 abundant in later ages. 



As the Orthoceras had never been met with in the marine Mus- 

 chelkalk, much surprise was naturally felt that 7 or 8 species of the 

 genus should appear in the Hallstadt beds, assuming these last to be- 

 long to the Upper Trias. Among these species are some of large di- 

 mensions, associated with large Ammonites with foliated lobes, a form 

 never seen before so low in the series, while the Orthoceras had never 

 been seen so high. But the latter genus has also been met with in 

 the Adnet, or lias strata of Austria, as I was assured in 1856 by several 

 eminent geologists of Germany. 



Professor Ramsay has lately made a careful analysis of the lists giv- 

 en by Bronn of 104 genera and 774 species of fossils, derived from the 

 St. Cassian beds, of all classes of the animal kingdom, nearly the whole 

 of them invertebrata ; and he has also made an analysis of another list 

 of 79 genera and 427 species of fossils from the same beds, drawn up 

 by a skilful naturalist, the late Count Munster. The results arrived at 

 in both cases agree very closely, proving that somewhat less that one- 

 third of the St. Cassian fossils have a primary or palaeozoic, and two- 

 thirds of them a secondary or mesozoic character. There would be 

 nothing wonderful or anomalous in such a result, were it not that the 

 fossils of the Muschelkalk, which arc supposed to be older than the 

 St. Cassian beds, contain a comparatively small proportion of primary 

 types, so that a palaeontologist would naturally presume, says Professor 

 Ramsay, that the St. Cassian beds were a stage nearer in time than is 

 the Muschelkalk to the Permian period. Bronn, accordingly, in draw- 

 ing up his catalogue, placed the St. Cassian beds in that position, or 

 as intermediate between the Bunter-sandstein and the Upper Per- 

 mian, or Zeckstein. It must, I think, be admitted that, were we not 



